Roof supports for mine workings

ABSTRACT

The invention provides a mine roof support in which centering of the outer part of a two-part base element with respect to a longitudinally extending medial reference axis is effected by contact faces which are mutually convergent, as viewed in plan, in a direction towards the forward end of the support, and are formed on two centering elements carried by a longitudinally movable guide element provided on the base of the support, and including a bracket for connection to a conveyor or other transversely extending anchor member at its forward end, these contact faces being presented inwardly and situated close to the reference axis to minimize the transmission of torque about the reference axis to the longitudinally movable guide element due to random vertical friction forces established between the contact faces and the part of the base element engaged thereby during the centering operation.

United States Patent [72] lnventor Karl Maria Groetschel Stolzestrasse 44, 463, Bochum, Germany [21] Appl. No. 867,329 [22] Filed Oct. 17, 1969 [45] Patented Sept. 7, 1971 [32] Priority Oct. 17, 1968 [33] Great Britain [3 ll 49359/68 [54] ROOF SUPPORTS FOR MlNE WORKlNGS 6 Claims, 5 Drawing Figs.

52 us. Cl... 61/45 [5 l] Int. Cl E2ld 15/44 [50] Field of Search 61/45 D; 248/357; 299/33, 31; 91/170 MP, 411, 412, 413, i 414 [56] References Cited UNITED STATES PATENTS 3,328,966 7/1967 Crevels et al. 61/45 D 3,431,738 3/1969 Groetschel 61/45 D 3,435,620 4/1969 Weirich et al. 61/45 D 3,448,584 6/1969 Rieschel 3,478,522 11/1969 Rieschel Primary ExaminerDennis L. Taylor Att0rney-Spencer & Kaye ABSTRACT: The invention provides a mine roof support in which centering of the outer part of a two-part base element with respect to a longitudinally extending medial reference axis is effected by contact faces which are mutually convergent, as viewed in plan, in a direction towards the forward end of the support, and are formed on two centering elements carried by a longitudinally movable guide element provided on the base of the support, and including a bracket for connection to a conveyor or other transversely extending anchor member at its forward end, these contact faces being presented-inwardly and situated close to the reference axis to minimize the transmission of torque about the reference axis to the longitudinally movable guide element due to random vertical friction forces established between the contact faces and the part of the base element engaged thereby during the centering operation.

PATEHTEUSEP 711m 3,603,098

sum 1 or 2 Fl -a. 2.

INVENTOR. Karl Mario Groe'rschel ATTORNEYS.

PATENTEDSEP nan 35031198 SHEET 2 0F 2 5' 2.7 cm 5. 3b Kzrl Morio ($135228! a, l

ATTORNEYS.

ROOF SUPPORTS FOR MINE WORKINGS CROSS-REFERENCES TO RELATED APPLICATIONS The present invention is a development of the invention described and claimed in my copending application Ser. No. 682,867 filed Nov. 14, 1967.

BACKGROUND OF THE INVENTION Field of the Invention This invention relates to roof supports primarily for use in underground mine workings of the kind comprising a bottom structure or base (herein called a base) for resting on the floor, a top structure or superstructure (herein called a superstructure) for engaging and supporting the roof, a plurality of power-operated extensible props extending between the base and superstructure, and traction means for advancing the support. Such supports are hereinafter referred to as being of the kind specified.

Description of the Prior Art In my copending application Ser. No. 682,867 as above mentioned, I have described and claimed a roof support of the kind specified wherein the base comprises inner and outer base elements from which respective parts of the superstructure are supported by respectively associated props, in each case spaced apart longitudinally of the support, and wherein the outer base element has laterally spaced side members affording between them a gap extending longitudinally of a longitudinal reference axis of the support and connected to each other at opposite ends of the gap, and the inner base element is of a length shorter than that of the gap, disposed in said gap, movable therealong by the traction means, and is of a width to be capable of lateral movement relatively to the outer base element in a plane generally parallel to the floor, and wherein the relative position of the base elements in a direction laterally of said reference axis is controlled by adjustable guide means acting between the base elements. I have further specifically described and claimed an arrangement wherein the traction means serve to advance the base elements altematively, and the guide means comprises centralizing means acting effectively between the base elements constraining these to a predetermined lateral position upon completion of the advancement step of one of said base elements.

In one form of the support as described and claimed I have provided an adjustable guide device which comprises a longitudinally movable element on one of two parts or elements of the base of the support which are interleaved with each other laterally of the support and have lateral clearance with respect to each other to enable them to undergo relative angular movement in a plane generally parallel to the floor and roof, the longitudinally movable guide element being so mounted as to be capable of being moved along a path of advancement which is parallel to, or which diverges to the left or right of, a longitudinally extending reference axis of the support and to cooperate with the other part or element of the base upon advancement of the latter to determine the angular relationship between the two parts. As disclosed, the longitudinally movable guide element includes means for connecting it to a conveyor or other anchor member extending transversely of the direction of advancement of the support forwardly thereof at any of a plurality of positions spaced apart along such anchor member and in such a manner as to retain the longitudinally movable element in parallel or divergent relation to said reference axis as aforesaid.

Also I disclosed an arrangement where one part of the base, namely the outer base element, and the longitudinally movable element were adapted to cooperate with each other through the intermediary of centralizing means during the final stages of advancement of said outer base element in order to bring the forward end of the latter into a predetermined lateral relation with respect to the forward end of said longitudinally movable element. Specifically the longitudinally extending guide element disclosed comprised laterally spaced guide rods slidable in guideways afforded by the inner base element with sufficient lateral clearance to permit of forward movement of the guide rods parallel to said reference axis or in divergent relation thereto to the left or right. Further, the centralizing means disclosed comprised elements, therein called cam elements, mounted at the outer sides of the guide rods and having outwardly presented contact faces arranged obliquely to the reference axis. These contact faces were engaged by the forward inner comers of said members of the outer base element.

While this arrangement has been found to provide effective centering of the outer base element with respect to the longitudinally movable guide element, conditions can arise in which torque is applied to the longitudinally movable guide element about a longitudinally extending axis passing medially through the means connecting said element to the conveyor or anchor member. Such torque can reach high values sufficient to cause damage to the connection means or to the anchorage member, or both.

The principal object of the present invention is to provide an improved arrangement. Such arrangement is applicable not only to roof supports of the kind specified as claimed in my copending application aforesaid wherein the base comprises laterally interleaved parts movable longitudinally relatively to each other, such as an outer base element and an inner base element, with clearance sufficient to provide for relative angular movement between the inner and outer base elements in a plane parallel to the floor, but is applicable also generally to roof supports of the kind specified whether the base element is formed in two parts or not.

SUMMARY OF THE INVENTION,

According to the invention a roof support of the kind specified is provided wherein the base is equipped with a longitudinally movable guide element provided at its forward end with means for connecting it to an anchor member such as a conveyor, cable, or rail extending transversely of the support forwardly thereof, and wherein centralizing means operative during the final stage of advancement of the base or a part thereof relative to the longitudinally extending guide element comprises cooperative centering elements disposed respectively on the longitudinally movable guide element and on the base or said part thereof respectively, and having respective contact faces formed to apply corrective lateral displacement to the base or said part relatively to the guide element, and which, in order to minimize or limit the application of torque to the guide element and hence to the anchor member about a longitudinal axis passing medially through said connection means, are disposed close to said axis.

The longitudinally movable guide element may, and preferably does, comprise laterally spaced guide rods (which term is used generically to denote any suitable form of elongated bar or tube), such guide rods being connected to each other at their forward ends and also with said connection means which is disposed centrally, or approximately centrally, between them, the centering element or respective centering elements provided on the guide rods presenting contact faces which are disposed one on each side of the medial longitudinally extending axis between such axis and the guide rods themselves.

The preferred arrangement is one wherein the contacts faces on the centering element provided on the longitudinally movable guide element are mutually convergent in a direction towards the forward end of the longitudinally movable guide element and face inwardly towards said medial axis.

With cam or centering elements disposed at the outer side of the guide rods in accordance with my prior proposal, any forces developing between the contact faces of these elements and the contact faces of the cooperative elements, that is to say the side members of the outer base element, in a direction perpendicular to the floor of the working (i.e. upwardly or downwardly), gave rise to a torque on the longitudinally movable guide element as a whole. The length of the radius arm of the torque-applying coupling was equal to the distance between the medial axis of the connection means and the point of engagement of the outer base element with the contact face of thecentering element in operation at theouter side of one of the guide rods. This radius arm was long enough to give rise to a value of torque which cancause damageas previously mentioned.

Further, angular deflection of the longitudinally movable guide element about saidmedial axis resulting from the torque tended to result in an increase in the value of torque applied-in this manner, since progressively there is brought into operation a further torque component resulting from the inward lateral-pressure exerted by the outer base element which now acts either above or below the medial axis.

With this arrangement according to the present invention on the other hand, the contact faces of thecenten'ng elements on the longitudinally movable guide element are arranged close to the medial axis, sothat initial angular deflection about the medial axis, due to forces perpendicular to the floor of the mine working'between the contact faces of cooperative cen.- tering elements, act through only a short radius a'rm and'thevalue of torque is wellable to be resisted withoutdamage by the connectionzmeans and by the anchor member. Moreover,

any angular deflection whichdoestake place about the medial axistends :to produce a progressively increasing corrective component of-torque turning the longitudinally movable guide member into-a plane in which laterally applied thrust from the cession by said traction,=means.-One advantageous form of such support is that in which the 'baseincludes an outer base element havinglaterally-spaced side members connectedto each other and affording alongitudinally extending gap between them, andan inner base element disposed in said gap: and having lateral clearance'with respect to the side members of the outer base element, theinner and outer baseelements each carrying longitudinally spaced props serving to support a' respective part of the superstructure, which parts also have lateral clearance space between them. Withthis arrangement,

due to the narrower width'of the inner base element, it is more difficult to ensure lateral angular stability for the inner base element in mine workings wherein the floor (and roof) slopes laterally. Consequently some lateral angular. deflection of the inner base element during the time at which the part of the superstructure carried thereby is outof load-bearing relation with the roof, that is to say during advancement of the inner Afurther aspect of the present invention concerns a roof support of the kind referred to in the preceding paragraph and resides in the arrangement whereby the inner baseelement is arranged to cooperate through the centering-means of the longitudinally movable guide element withthe latter when in its rearward or contracted position, and further centering means are provided operative-between the two base elements at a level higherthan the first said-centering means, so as to act, in combination, as an erecting stabilizing means tending to correct lateral angular displacement of the inner part of the support during the final stage of its advancement.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example, with reference to the accompanying drawings wherein:

FIG. l is a planview of a roof support of the-kind'specified (the superstructure being shown-onlygin chain lines) provided with one embodiment of longitudinally movable guide element andcentering'meansin accordancewith the invention, the parts being shown with the longitudinally movable guide element in its advanced or extended position;

FIG. 2 is a plan view similar to FIG.'1 but with the longitudinally movable guide element in its contracted position after advancement of the 'outer base element;

FIG. 3 is a fragmentary view in front elevation and in cross section on the line 33 of FIG. 1;

FIG. 4 is a diagrammatic view in front elevation illustrating the forces which may be applied to the longitudinally movable guide element through-the centering means thereof with the prior arrangement as disclosed in my copending application Ser. No. 682,867 filed Nov. 14, 1967; and

FIG. 5 is a view corresponding to FIG. 4 showing'the'forces which may arise with the embodiment illustrated in FIGS. 1 and 2.

DETAILED DESCRIPTION Thesupport may-be constructed generally as disclosed in mycopending application Ser. No. 682,867 filedNov. I4, 1967 and in particular as illustrated in, and described with reference to; FIGS. 5.to 7 thereof. For convenience it is noted that the support comprises a base including'an outer base.ele-- ment formed of two side members 10 each conveniently formedof two laterally spaced bars of box section secured to top and bottom ,plates' by welding; thetop plates 7 having secured thereto upstanding socketlike chambers -l-l at the rear end and 12 at theforward end of the support. Chambers-at correspondingends:arerigidly connected with each-other by cross members 13 and '14 whichare preferably-welded respec tively to chambers 11 and 12..

The base :element further includes an inner baseelement- 15 e shorter thanthe gap afforded by theouter base element and:-

movable therealong by atraction-ram l5a. The inner base element-is a fabricated structure of laterally-spacedinwardly extending plates. Theremay be'two such outer plates and two such inner plateswelded to top-and'bottom plates to form-two laterally spaced, approximately box section, girders-spanned at their. forward and rearward ends by socketlike chambers 16 and 17;

The superstructure (shown in chain lines in outline in FIGS, 1 and 2) also comprises an outer part which includes side members-l8 each formed of a pair of laterally spaced roofbarsof box section. The side members 18 are rigidly connected witheach other adjacent the:rearward end of the support and :at aposition above the forward'end of the base by crossmemhers 18a, the central portions of which are cranked'or offset downwardly below. the side members 18 to'define in conjunction therewith-a channel or passageway 18b.

The superstructure. further comprises an inner part 19.

similar in construction to the sidemembers l8 and disposed in this channel or passageway. The inner and outer parts of the superstructure may be of the same, or approximately the same, length.

' In use the extent of forward projection of both the inner and outer parts of the superstructure is such as to enable it toproject forwardly to support the roof of a mine working extending along and adjacent to the coal face, over a conveyor 20, when the support is used as intended in the method .of long wall coal mining. A coal-getting machine,(not shown) travels along a guideway afforded by side members of the conveyor and discharges coal onto the conveyor..

The outer part of the superstructure is supported by longitudinally spaced props 21 and 22 in the socketlike chambers "11 and 12 of the outer base element. The inner part of the top structure is supported by props 23 and 24 in the socketlike chambersl6 and [7 of the inner base element. The chambers form seatings in the base for the reception of the props, and corresponding seatings at longitudinally spaced positions are provided for reception of the prop heads on both the inner and outer parts of the superstructure.

The props are hydraulic props which may be supplied with hydraulic fluid under pressure from a motor-driven pump or possibly from a manually or foot-operated pump. 7

As will be seen from the drawings, clearance spaces exist between the side members 10 of the outer base element and the inner base element and similar clearance spaces exist between the inner part 19 and the outer parts 18 of the superstructure. It is thus possible for relative angular movement to take place between the inner part of the support comprising the inner base element, its longitudinally spaced props, and inner part of the superstructure with respect to the outer part of the support, namely the outer base element, its longitudinally spaced props and the outer part of the superstructure.

To enable such movement to be effected when required longitudinally spaced guide devices are provided, these being indicated generally at 25 and 26.

The guide device 25 is in the form of a vertical plate which is some embodiments of the support is associated with an actuating means for shifting it laterally relatively to the inner base element at the rear end of which it is mounted but which, in the present embodiment, is maintained in a fixed position, either by fixture to the inner base element or by locking of the actuating means (not shown in detail), but possibly constructed arid arranged as disclosed in my copending application already mentioned.

The guide device 26 is adjustable and comprises a guide element movable longitudinally of the support relatively to the base thereof. Such guide element, as shown, preferably comprises laterally spaced guide rods 27 slidable in the guideways already mentioned and afforded by the inner base element. Such guideways are of sufficient width to permit of the guide rods being set parallel to the reference axis 28 or selectively to the' left or right thereof, which last-mentioned condition is shown in FIG. 1.

The longitudinally movable guide element includes a crossmember 29 rigidly connecting the guide rods to each other at their forward ends. Conveniently the connection means is also provided on said crossmember centrally between the guide rods or approximately so. Such connection means comprises a bracket 30 which may be in the form of a claw interlocked with a rail extending longitudinally of the conveyor and clamped or held by positive means in a predetermined position therealong. Alternatively, as shown, the conveyor may have a rail 31 formed with a plurality of holes permitting of the passage of a connecting pin through the bracket 30 and through a selective one of the holes indicated generally at 32.

Alternatively, in some cases the conveyor need not be used as the anchor member. A cable or rail separate from the conveyor could be provided for this purpose. The conveyor or such cable or rail may be connected to means for moving it lengthwise, that is transversely of the reference axis 28, to permit of collective adjustment of the forward ends of all the adjustable guide devices such as 26 connected thereto.

The adjustable guide device 26 cooperates with both the inner base element and the outer base element at different stages of advancement of the support, as hereinafter described, through the intermediary of centering means. The centering means includes centering elements disposed on the guide device 26 and on the two base elements respectively, and such centering means operates in the final stage of advancement of each element of the base, the base element concerned being free to undergo some angular and lateral displacement at its forward end during the remaining part of its forward travel, that is from the beginning of the forward travel until there is cooperation between the centering elements of the guide device 26 and that or those provided on the base element concerned.

The centering elements on the guide device 26 are indicated respectively at 33 and are secured rigidly, and, if desired, adjustably so as to enable their lateral positions to be varied, in any convenient manner to the crossmember 29 and to the guide rods 27, and are disposed at the inner sides of the latter as will be evident in FIGS. 1 and 2.

Each centering element 33 presents two contract contact faces. The contact faces 34 are presented inwardly towards a medial axis A through the point of connection between the bracket 30 and the conveyor and are mutually convergent in a direction towards the forward ends of the guide rods. These contact faces cooperate with a centering element 35 on the outer base element and conveniently in the form of an arm secured to the crossmember 14 at the forward end of the outer base element and extending downwardly therefrom between the guide rods.

The other contact faces 36 of the centering elements 33 are mutually divergent in a direction towards the forward ends of the guide rods and cooperate with portions of the outer base element which act as centering elements thereof, namely the forward margins of the two inner vertical plates 15b which form the inner boundaries of the two guideways through which the rods 27 extend.

Also provided on the base of the support are further centering elements situated at a level above the centering elements 33 and operative between the outer base element and inner base element to effect erection of the latter in combination with the centering elements 33.

These further centering elements are indicated at 37 and may conveniently be mounted on the socketlike chambers 12 as near the upper ends of the latter as possible. The centering elements 37 have contact faces 38 which are mutually convergent in a direction towards the forward end of the support and are engaged by the forward corners of the socketlike chamber 17 of the inner base element which act as the cooperative centering elements.

It will be noted that the centering elements 33 are disposed closely adjacent to the floor of the mine working, that is at only a short distance upwardly from the undersurface of the base, while the socketlike chamber 17 may be of appreciable height, typically extending to a position about midway between the base and the superstructure when the latter is in its lowered position (as will be the case during advancement of the inner part of the support). The centering forces exerted respectively by the centering elements 33 and 37 are thus spaced apart vertically by an appreciable distance, thereby exerting a high restoring torque to correct lateral angular displacement of the inner part of the support without giving rise to very high stresses in the material of the centering elements themselves. This minimizes wear.

In operation of the support the parts are initially as seen in FIG. 2 and after passage of the coal-getting machine, but before the conveyor can be snaked or advanced towards the coal face due to laterally proximity of the coal-getting machine, early support is furnished to the newly exposed roof by advancement of the inner part of the support to the position shown in FIG. I.

At this time the guide rods 27 of the guide device 26 will be in the retracted position, and although the lateral clearance between these guide rods and the guideways will provide freedom from angular movement in a plane parallel to the floor of the inner base element with respect to the outer base element, proper lateral positioning of the forward end of the inner base element will be achieved in the final stages of advancement through cooperation with the contact faces 36 of the centering elements 33 (then positioned immediately adjacent to the forward end of the base) and the portions of the inner base element which act as centering elements, namely the inner-plates 15b of the guideways. Alternatively supplementary plates secured between the top and bottom plates of the inner base element could be provided to present the required contact faces if more convenient. Such supplementary plates may be disposed at the inner sides of the vertical plates which form the inner walls of respective guideways. The supplementary plates present inwardly facing contact faces which, if desired, may be mutually divergent in a direction towards the forward end of the inner base element, for example in conformity with the divergence presented by the contact faces 36 of the centering elements 33. Also, if desired, the

supplementary plates may have an inclination laterally outwardly from their lower to their upper ends.

Alternatively the supplementary plates and the plates which form the inner boundary of each guideway may together define cavities open at their forward ends for reception of the rearwardly presented tapered ends of the centering elements 33.

If the working presents a lateral inclination and there is lateral angular deflection of the inner part of the support during advancement, this too will be corrected during the final stage of advancement by the combination of the centering elements 33 and 37 acting as already described. Therefore, preparatory to reextension of its props 23 and 24, the inner base element will be properly centered relative to the outer base element and also held in perpendicular, or approximately perpendicular, relation to the floor of the mine working.

When the coal-getting machine has travelled sufficiently far beyond the support to be removed from the conveyor section to which the guide device 26 is connected, such conveyor section can be advanced towards the newly exposed coal face by a traction ram provided on the support (not shown) or on a selected number only of the supports in a given row or installation.

This draws the longitudinally movable guide element or guide device 26 forwardly as seen in FIG. 1 and the position of the forward end thereof is determined by the lateral position of the conveyor or anchor member which, as already indicated, may be adjusted if necessary.

Advancement of the outer part of the support is now effected with its props contracted and in the final stage centering of the outer part of the support takes place by engagement with the contact faces 34 and the downwardly extending centering element 35. The position of the parts is now again as seen in FIG. 2.

The fixed guide element 25 at the rearward end of the inner base element controls the lateral. position of this end of the inner base element-at all stages of advancement.

The difference in the conditions of operation of the centering elements increase with the present invention and the cam elements'performing a similar, but not identical, function as disclosed in my copending application Ser. No. 682,867 filed Nov. 14, I967, is illustrated in FIGS. 4 and 5.

FIG. 4 illustrates operation of the cam copending application.

In a mine working having an inclination laterally of the support the forward end of one of the side members. 710 of the outer base element at the higher side of the working will be in contact with the cam element 786 at the outer side of the higher guide rod 783 during the final stages of advancement of the outer base element. I 1

If a vertical force represented by F develops between the contact face of the cam element (acting similarly to the centering element of the present construction) 786 and the side member 710, for example in an upward direction as shown, the guide rods collectively will tend to be rotated in an anticlockwise direction about the medial axis A. This will cause contact between the side member 710 and the contact face of the cam element to be concentrated in a region adjacent to the lower outer comer of the latter, and a lateral force F,, due to the weight of the outer base element acting downwardly with respect to the inclination of the floor, will be applied at this position.

If the value of the upward force F should produce a suffcient anticlockwise rotation of the guide rods, the force F will no longer exert a restoring torque since the torque arm represented by the distance c will reduce to zero as the cam element 786 rises and will thereafter lie above the axis B passing transversely through the medial axis A so that the lateral force F, then actually tends to aid or accentuate the torque tending to rotate the guide rods collectively about the axis A in an anticlockwise direction.

Such conditions can give rise to very high values of torque with the disadvantageous effects already mentioned.

elements of my FIG, 5 represents diagrammatically the conditions applicable to the support illustrated in FIGS. 1 and 2. ln this case the force P, which tends to produce clockwise rotation of the guide rods 27 collectively acts as a radius b which is much less than the'radius a shown in FIG. 4. Therefore, the value of the ing element 33. The force F exerts a restoring or corrective" torque through radius arm having a dimension c which initially has the same value as that shown in FIG. 4. However, any tendency to increase the angular deflection of the guide rods about the axis A in a clockwise direction produces an increase in the restoring torque because the radius arm c in-' creases in value.

Therefore, the arrangement of the invention not only provides smaller torque forces tending to turn the guide rods collectively about the axis A, but avoids entirely the situation whereby the lateral thrust of the outer base element accentuates or aids this torque and substitutes a condition wherein an increasing value of restoring torque F Xc is applied.

lclaim:

1. In a support for supporting the roof of a mine working comprisin'gz a. a base for resting on the floor,

b. a superstructure for engaging and supporting the roof,

c. a plurality of power-operated extensible props extending between said base and said superstructure,

d. traction means for advancing said support, the improvement wherein:

e. said base includes a longitudinally movable guide element having means at a forward end thereof for connecting said guide element to an anchor member extending transversely of said support at a position forwardly thereof,

f. centralizing means are provided for applying corrective lateral displacement to at least part of said base relative to said guide element over a terminal portion of an advancement step imparted to said part of said base by said traction means, said centralizing means comprises cooperative centering elements disposed respectively on said longitudinally movable guide element and on said part of said base respectively, and having respective contact faces formed to apply said corrective lateral displacement,

. said contact faces being disposed close to a reference axis extending longitudinally of said support and medially through said connection means, whereby the application of torque about said axis to said longitudinally movable guide element and hence to said anchor means is minimized.

2. A support according to claim 1 wherein:

a. said longitudinally movable guide element comprises laterally spaced guide rods connected to each other at their forward ends and also to said connection means,

b. said connection means is disposed at least approximately centrally between said guide rods,

c. respective ones of said centering elements are provided on said guide rods and present respective contact faces disposed one on each side of said reference axis between such axis and the guide rods themselves.

3. A support according to claim 2 wherein said contact faces on said centering elements provided on said longitudinally movable guide element are mutually convergent in a direction towards the forward end of said longitudinally movable guide element and face inwardly towards said reference axis. 1

4. A support according to claim 1 wherein:

a. at least said base includes longitudinally extending parts disposed in interleaved relation with each other in a direction laterally of the support,

b. said parts are operativryco nnected with each other by said traction means for respective advancement thereby in successive steps,

c. said parts are spaced laterally from each other to define an interpart clearance space providing capability of limited movement of one of said parts relatively to the other in a direction transversely of said support,

d. said base further includes a longitudinally movable guide element provided at its forward end with means for connecting it to an anchor means extending transversely of the support and situated forwardly thereof,

e. said centering elements are provided on each of said parts of said base to cooperate with other ones of said centering elements on said longitudinally extending guide element to bring each of said parts of said base to a predetermined relative lateral position with respect to said longitudinally extending guide element over a terminal portion of an advancement step of each of said parts A support according to claim 4 wherein said centering elements on said movable guide element include:

a. one pair of contact faces which are mutually convergent in a direction towards the forward end of said longitudinally movable guide element and face inwardly towards a reference axis extending longitudinally of said support and passing medially through said connection means, this pair of contact faces cooperating with an outer one of said parts of said base,

. a further pair of contact faces which are mutually divergent in a direction towards the forward end of said longitudinally movable guide element and are presented in a direction outwardly of said reference axis and cooperate with an inner one of said parts of said base.

A support according to claim 4 wherein: the inner of said parts of said base cooperate with said centering means of said longitudinally movable guide element when the latter is in a rearward or contracted position relative to said base,

. further centering means are provided operative between 

1. In a supporT for supporting the roof of a mine working comprising: a. a base for resting on the floor, b. a superstructure for engaging and supporting the roof, c. a plurality of power-operated extensible props extending between said base and said superstructure, d. traction means for advancing said support, the improvement wherein: e. said base includes a longitudinally movable guide element having means at a forward end thereof for connecting said guide element to an anchor member extending transversely of said support at a position forwardly thereof, f. centralizing means are provided for applying corrective lateral displacement to at least part of said base relative to said guide element over a terminal portion of an advancement step imparted to said part of said base by said traction means, g. said centralizing means comprises cooperative centering elements disposed respectively on said longitudinally movable guide element and on said part of said base respectively, and having respective contact faces formed to apply said corrective lateral displacement, h. said contact faces being disposed close to a reference axis extending longitudinally of said support and medially through said connection means, whereby the application of torque about said axis to said longitudinally movable guide element and hence to said anchor means is minimized.
 2. A support according to claim 1 wherein: a. said longitudinally movable guide element comprises laterally spaced guide rods connected to each other at their forward ends and also to said connection means, b. said connection means is disposed at least approximately centrally between said guide rods, c. respective ones of said centering elements are provided on said guide rods and present respective contact faces disposed one on each side of said reference axis between such axis and the guide rods themselves.
 3. A support according to claim 2 wherein said contact faces on said centering elements provided on said longitudinally movable guide element are mutually convergent in a direction towards the forward end of said longitudinally movable guide element and face inwardly towards said reference axis.
 4. A support according to claim 1 wherein: a. at least said base includes longitudinally extending parts disposed in interleaved relation with each other in a direction laterally of the support, b. said parts are operatively connected with each other by said traction means for respective advancement thereby in successive steps, c. said parts are spaced laterally from each other to define an interpart clearance space providing capability of limited movement of one of said parts relatively to the other in a direction transversely of said support, d. said base further includes a longitudinally movable guide element provided at its forward end with means for connecting it to an anchor means extending transversely of the support and situated forwardly thereof, e. said centering elements are provided on each of said parts of said base to cooperate with other ones of said centering elements on said longitudinally extending guide element to bring each of said parts of said base to a predetermined relative lateral position with respect to said longitudinally extending guide element over a terminal portion of an advancement step of each of said parts.
 5. A support according to claim 4 wherein said centering elements on said movable guide element include: a. one pair of contact faces which are mutually convergent in a direction towards the forward end of said longitudinally movable guide element and face inwardly towards a reference axis extending longitudinally of said support and passing medially through said connection means, this pair of contact faces cooperating with an outer one of said parts of said base, b. a further pair of contact faces which are mutually divergent in a direction towards the forward end of said longitudinally movable guide element And are presented in a direction outwardly of said reference axis and cooperate with an inner one of said parts of said base.
 6. A support according to claim 4 wherein: a. the inner of said parts of said base cooperate with said centering means of said longitudinally movable guide element when the latter is in a rearward or contracted position relative to said base, b. further centering means are provided operative between said two parts of said base and mounted on said base at a level higher than the first said centering means, so as to act in combination with the latter as an erecting stabilizing means tending to correct relative lateral angular displacement between said parts of said base and hence between props and respective parts of said superstructure carried by said inner parts of said base. 